INSECTS INJURIOUS TO CONIFERS. 73 



4. Defoliation renders a tree liable to the attacks of other insects, 

 especially of the much-dreaded bark -beetles, which have so often 

 completed the havoc begun in European forests by hordes of caterpillars. 

 Damage by storm, snowfall, frost, or by forest h'res or caterpillar- 

 defoliation, together with careless forestry and the slovenly accumulation of 

 loppings, felled timber and unbarked logs, serve to foster the development 

 of such insects till serious injury is risked. The thin-barked Spruce 

 suffers more than the Pine, and it was the forests of this tree that 

 were so terribly ravaged by barkd)eetles in the Harz Mountains during 

 the last century. Except the Pine-beetle (Myelophilus piniperda), no 

 bark-beetles cause extensive damage in Great Britain ; still many 

 injurious kinds do occur which might cause trouble if the circumstances 

 which favour them be disregarded through over-confidence in their 

 supposed innocuousness. Every forest tree cannot possibly be in a 

 perpetual state of robust health, and there is one period when every 

 tree is liable to -insect-attacks after transplantation. 



5. Not a few insects feed during some part of their lives on or 

 in the young shoots of Conifers, in the leader or the extremities of 

 the lateral branches. When the leader perishes the upward growth is 

 checked until one or more branches of the top whorl twist round to 

 supply its place. So lateral branches are destroyed or have their 

 growth stopped, and the tree becomes altered in shape and appearance. 

 Such mutilated Pines abound in almost all woods in the South of 

 England. 



6. The practice of growing large pure woods of Conifers of uniform 

 age tends especially to widespread ravages. Most Conifer-feeding 

 insects will not touch deciduous trees, and many are confined to a 

 single species of Conifer. Others, again, limit their attacks almost 

 completely to a single period in the life of a tree. Hylolrius alnetis 

 is very destructive to trees under seven years old, comparatively 

 harmless to those of ten or more years. In a pure wood, the 

 conditions favourable to increase of an insect pest exist over the whole 

 area at once, and there is no limit to the supply of food, the 

 facilities for egg-laying or for migration to fresh districts from the 

 part infected. 



Wire iron it*. Seedling Conifers, if the nursery be placed in a well- 

 chosen situation, secure from the inroads of Hyloliu* abietis, are 

 usually exempt from the attacks of special Conifer-feeding insects. 

 Their chief enemies are the polyphagous w T ireworms, the larvse of the 

 " click-beetles," and the grubs of the cockchafer. Wire worms occasionally 

 do much harm in ground newly broken for nursery purposes. The 

 damage lessens when the ground has been cultivated for some time, 

 for the destruction during the first year or two is due to wire- 

 \vonns which, having sprung from eggs laid before the bed was 

 formed, exist already in the soil. When trees are actually growing 

 there the parent beetles lay eggs less readily or not at all, and thus 

 the bed is gradually cleansed. When very young Conifers are 

 attacked they are gnawed completely through just above the roots, 

 and such cut plants sometimes strew the bed. Seeds are also destroyed 

 before germination. 



It is desirable to examine the ground selected for the nursery, and 

 to reject the plot if it appears badly infested, or to cleanse it 

 thoroughly before planting. As the acreage required is small, there 



